Applied Geochemistry (v.32, #C)
Preface by Neus Otero; Thomas Bullen (1-2).
Carbon and oxygen-isotope stratigraphy of the Early Cretaceous carbonate platform of Pădurea Craiului (Apuseni Mountains, Romania): A chemostratigraphic correlation and paleoenvironmental tool by Delia Cristina Papp; Ioan Cociuba; Daniel Florin Lazăr (3-16).
► Carbon and oxygen-isotope variations in carbonate rocks were investigated. ► Major perturbations of the carbon and oxygen cycles were identified. ► Two major oceanic anoxic events were recognized. ► The positive and negative anomalies are used for stratigraphic correlation.Stable C and O isotope records were obtained from carbonate rocks spanning the Hauterivian to Cenomanian interval collected in several sections from the carbonate platform of Pădurea Craiului (Apuseni Mountains, Romania). In the absence of some key biostratigraphic marker species, stable isotopes were applied as a tool for stratigraphic correlation and dating. The composite δ13C and δ18O curves for the Early Cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes. The Hauterivian and the Barremian limestones (Blid Formation) display lower δ13C values (−2.8‰ to +2.9‰) relative to the Aptian–Albian deposits (−2.6‰ to +5.4‰) (Ecleja, Valea Măgurii and Vârciorog Formations). The red detrital formation (Albian–Cenomanian) is characterized by a highly variable distribution of the δ13C values (−3.5‰ to +3.9‰). Based on the similarities between the C-isotope curve established in Pădurea Craiului and from other sections in the Tethyan and the Pacific regions, two major oceanic anoxic events characterized by δ13C positive excursions were clearly recognized. The first is the OAE1a event (Early Aptian) in the upper part of the Ecleja Formation and the Valea Măgurii Formation. The second is the OAE1b event (Late Aptian–Albian) in the upper part of the Vârciorog Formation and in the Subpiatră Member. The position of the Aptian/Albian boundary is estimated to be at the upper part of the Vârciorog Formation, immediately after the beginning of the δ13C positive excursion. The δ13C data show major negative excursions during the Barremian (Blid Formation), Early Aptian (Ecleja Formation), and Late Aptian (Vârciorog Formation). The O isotope variation pattern (−10.2‰ to −2.1‰) is consistent with progressively warming temperatures during the Early Barremian followed by a cooling period. A subsequent warming period culminated in the Early Aptian. A significant cooling phase corresponds to the Late Aptian and Early Albian and the climate cooled again during the Late Albian and into the Early Cenomanian stage. The data provide a better understanding of the Early Cretaceous sedimentation cycles in Pădurea Craiului and create a more reliable framework for regional correlations.
Boron, lithium and methane isotope composition of hyperalkaline waters (Northern Apennines, Italy): Terrestrial serpentinization or mixing with brine? by Tiziano Boschetti; Giuseppe Etiope; Maddalena Pennisi; Millot Romain; Lorenzo Toscani (17-25).
► First data on boron and lithium isotope on waters from ophiolites are described. ► High boron and lithium isotope composition may be related to terrestrial serpentinization. ► Methane isotope data show unusual biotic signature.Spring waters issuing from serpentinized ultramafic rocks of the Taro-Ceno Valleys (Northern Apennine, Emilia-Romagna region, Italy) were analyzed for major element, trace element and dissolved gas concentrations and δ11B, δ7Li, δ18O(H2O), δ2H(H2O), δ13C(CH4) and δ2H(CH4) isotope compositions. Similar to other springs worldwide that issue from serpentinites, the chemical composition of the waters evolves with water–rock interaction from Ca-HCO3, through Mg-HCO3 and ultimately to a hyperalkaline Na-(Ca)-OH composition. Most of the Ca- and Mg-HCO3 springs have δ11B ranging between +16.3‰ and +23.7‰, consistent with the range of low P–T serpentinites. Very high δ11B in two springs from Mt. Prinzera (PR10: +39‰; PR01: +43‰) can be related to isotopic fractionation during secondary phase precipitation, as also inferred from δ7Li values. In contrast to typical abiogenic isotope signatures of CH4 from serpentinized rocks, dissolved CH4 from the Taro-Ceno hyperalkaline springs has an apparent biotic (thermogenic and/or mixed thermogenic-microbial) signature with δ13C(CH4) ranging from −57.5‰ to −40.8‰, which is similar to that of hydrocarbons from production wells and natural seeps in adjacent hydrocarbon systems. The data suggest that CH4 in the hyperalkaline springs investigated in this study may derive from organic matter of the sedimentary (flysch and arenaceous) formations underlying the ophiolite unit. However, small amounts of H2 were detected in one hyperalkaline spring (PR10), but for two springs with very low CH4 concentrations (PR01 and UM15) the δ2H value could not be measured, so the occurrence of some abiotic CH4 cannot be excluded. The occurrence of thermogenic CH4 in ophiolites may be a widespread phenomenon, and thus the characterization of serpentinization-related gases requires accurate evaluation of the regional context including a careful knowledge of the relationships with surrounding sedimentary rocks and their hydrocarbon potential.
The carbon stable isotope biogeochemistry of streams, Taylor Valley, Antarctica by W.B. Lyons; D.L. Leslie; R.S. Harmon; K. Neumann; K.A. Welch; K.M. Bisson; D.M. McKnight (26-36).
► δ13C-DIC reported from McMurdo Dry Valleys, Antarctica, streams. ► Stream water δ13CPDB values range −9.4‰ to +5.1‰, largely inorganic in character. ► Atmospheric exchange is the dominant control on δ13C-DIC.The McMurdo Dry Valleys region of Antarctica is the largest ice-free region on the continent. This study reports the first C stable isotope measurements for dissolved inorganic C present in ephemeral streams in four dry valleys that flow for four to twelve weeks during the austral summer. One of these valleys, Taylor Valley, has been the focus of the McMurdo Dry Valleys Long-Term Ecological Research (MCM-LTER) program since 1993. Within Taylor Valley, numerous ephemeral streams deliver water to three perennially ice-covered, closed-basin lakes: Lake Fryxell, Lake Hoare, and Lake Bonney. The Onyx River in the Wright Valley, the longest river in Antarctica, flows for 40 km from the Wright Lower Glacier and Lake Brownworth at the foot of the glacier to Lake Vanda. Streamflow in the McMurdo Dry Valley streams is produced primarily from glacial melt, as there is no overland flow. However, hyporheic zone exchange can be a major hydrogeochemical process in these streams. Depending on landscape position, these streams vary in gradient, channel substrate, biomass abundance, and hyporheic zone extent. This study sampled streams from Taylor, Wright, Garwood, and Miers Valleys and conducted diurnal sampling of two streams of different character in Taylor Valley. In addition, transect sampling was undertaken of the Onyx River in Wright Valley. The δ13CPDB values from these streams span a range of greater than 14‰, from −9.4‰ to +5.1‰, with the majority of samples falling between −3‰ and +2‰, suggesting that the C stable isotope composition of dissolved C in McMurdo Dry Valley streams is largely inorganic in character. Because there are no vascular plants on this landscape and no groundwater input to these streams, atmospheric exchange is the dominant control on δ13C-DIC.
Characterisation and isotopic evolution of saline waters of the Outokumpu Deep Drill Hole, Finland – Implications for water origin and deep terrestrial biosphere by Riikka Kietäväinen; Lasse Ahonen; Ilmo T. Kukkonen; Nina Hendriksson; Mari Nyyssönen; Merja Itävaara (37-51).
► δ2H, δ18O, and 87Sr/86Sr of saline groundwater in bedrock down to 2.5 km depth. ► Separate water and typesisolated ecosystems at different depths. ► Water evolution modelled with silicate hydrolysis. ► Water origin: meteoric water recharged under warmer climate. ► Inferred residence times of groundwater tens of millions of years.The isotopic composition of water and dissolved Sr as well as other geochemical parameters at the 2516 m deep Outokumpu Deep Drill Hole, Finland were determined. The drill hole is hosted by Palaeoproterozoic turbiditic metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granitoids. Sodium–Ca–Cl and Ca–Na–Cl-rich waters (total dissolved solids up to ca. 70 g L−1) containing significant amounts of gas, mainly CH4 (up to 32 mmol L−1), N2 (up to 10 mmol L−1), H2 (up to 3.1 mmol L−1) and He (up to 1.1 mmol L−1) discharge from fracture zones into the drill hole. This water is distinct from the shallow fresh groundwater of the area, and has an isotopic composition typical of shield brines that have been modified during long-term water–rock interaction. Based on water stable isotopes and geochemistry, the drill hole water profile can be divided into five water types, each discharging from separate fracture systems and affected by the surrounding rocks. The δ2H varies from −90‰ to −56‰ (VSMOW) and δ18O from −13.5‰ to −10.4‰ (VSMOW), plotting clearly above the Global and Local Meteoric Water Lines on a δ2H vs. δ18O diagram. The 87Sr/86Sr ratios range between 0.72423 and 0.73668. Simple two-component mixing between 2H and 18O rich end-member brine and meteoric water cannot explain the water stable isotopic composition and trends observed. Instead, hydration of silicates by ancient groundwaters recharged under different climatic conditions, warmer than at present, is the most likely mechanism to have caused the variation of the δ2H and δ18O values. Water types correlate with changes in microbial communities implying that different ecosystems occur at different depths. The different water types and microbial populations have remained isolated from each other and from the surface for long periods of time, probably tens of millions of years.
Implications of sulfur isotope fractionation in fracture-filling sulfides in crystalline bedrock, Olkiluoto, Finland by E. Sahlstedt; J.A. Karhu; P. Pitkänen; M. Whitehouse (52-69).
► SIMS study of S isotopes in fracture-bound sulfides at Olkiluoto, Finland. ► Extreme range in δ34S values, from −50.4‰ to 82.1‰, obtained from fracture sulfides. ► Latest pyrite characterized by bacterial SO 4 2 - reduction and restricted SO 4 2 - input. ► SO 4 2 - -reservoirs replenished in pulses during latest pyrite precipitation event.A detailed investigation of 34S/32S ratios in fracture-bound pyrite and marcasite was conducted at Olkiluoto, western Finland, in order to gain information on paleohydrogeochemical conditions in a deep groundwater (0–400 m b.s.l.) environment. The bedrock at Olkiluoto is being considered for a final repository of spent nuclear fuel. The 34S/32S ratios were measured in situ on individual sulfide grains, using secondary ion mass spectrometry (SIMS) supplemented by analyses from bulk sulfide material. The δ34S values of pyrite and marcasite show considerable variations, from −50‰ to +82‰ VCDT. Using published records and new data from fracture filling minerals, the pyrite fillings were classified into groups representing distinct episodes of fracture mineral formation. The δ34S values of these groups record a transition from hydrothermal activity to a low temperature groundwater environment. The δ34S values of hydrothermal pyrite vary between −18‰ and +34‰. However, hydrothermal pyrite that definitively precipitated at 128–245 °C, evidenced by fluid inclusion data from co-genetic calcite, is characterized by a more limited variation in δ34S from −8.6‰ to +3.9‰. The high variability of δ34S within the hydrothermal pyrite precipitates indicates that biogenic fractionation effects cannot be completely excluded. Hydrothermal pyrite precipitation is likely related to hydrothermal systems produced by Mesoproterozoic rapakivi granite and diabase intrusions. Subsequent pyrite generations show a wider spread of δ34S values. Pyrite types representing formation temperatures from ca. 50 to 90 °C have δ34S values ranging from −40‰ to +82‰, and the latest low temperature (<80 °C) pyrite precipitates are characterized by δ34S from −50‰ to +78‰. The wide range of δ34S values is attributed to bacterial SO 4 2 - reduction, affected by Rayleigh fractionation under restricted SO 4 2 - input. It can be calculated that the highest δ34S values in pyrite represent consumption of ca. 90% of the original SO 4 2 - in the deep groundwater in a fracture section. Furthermore, in situ variations of the δ34S values in pyrite grains indicate that pulses of fresh SO 4 2 - with relatively non modified S-isotopic composition have periodically entered the fractures. The latest low temperature pyrite formation event most likely occurred during the Holocene period when brackish, SO 4 2 - -rich waters of the Litorina Sea infiltrated the fracture network at 8000–4000 BP, providing substrate for SO 4 2 - -reducing bacteria. Due to the complex Quaternary history of the site and low temperature conditions existing for millions of years, latest fracture filling calcite and pyrite may represent a compilation of several low temperature precipitation events. The records of δ13C in calcite and δ34S in coexisting pyrite indicate that paleogroundwaters have been influenced by the migration of a redox front between methanic and sulfidic environments. These findings can be used to consider the possible geochemical changes that may affect the materials used to contain spent nuclear fuel.
Isotopic signatures of otoliths and the stock structure of canary rockfish along the Washington and Oregon coast by Yongwen Gao; Russell A. Svec; Farron R. Wallace (70-75).
► Otoliths of 120 canary rockfish were analyzed for δ18O and δ13C. ► δ18O and δ13C values of the otoliths ranged from −0.2‰ to +1.7‰ and −5.4‰ to −1.4‰. ► No separation was observed from the isotopic data and δ18O vs. δ13C correlation. ► No significant difference was computed between WA and OR samples especially in δ13C. ► Canary rockfish may belong to a single spawning stock or population coast-wide.Canary rockfish are one of the commercially important rockfish species along the US Pacific coast. Yet little is known about their life history and stock structure. In this study 120 canary rockfish otoliths were collected from waters off the Washington and Oregon coast and subjected to stable O and C isotope (δ18O and δ13C) analyses. One powder sample was taken from the nucleus of each otolith, and the other from the 5th annual ring. Data from otolith nuclei can provide information on the natal sources and spawning stock separations, while data from age-1 to age-5 may indicate changes in fish habitat. Overall the δ18O values in otoliths of canary rockfish ranged from −0.2‰ to +1.7‰, whereas δ13C values of the same samples ranged from −5.4‰ to −1.4‰. The isotopic data and correlation of δ18O versus δ13C did not show clear separation between Washington and Oregon samples, similar to those for a previous study on yelloweye rockfish from the same region. These results suggest that canary rockfish may belong to a single spawning stock or population along the Washington and Oregon coast.
A preliminary carbon and nitrogen isotopic investigation of bone collagen from skeletal remains recovered from a Pre-Columbian burial site, Matanzas Province, Cuba by W.M. Buhay; Y. Chinique de Armas; R. Rodriguez Suárez; C. Arredondo; D.G. Smith; S.D. Armstrong; M. Roksandic (76-84).
► Collagen isotope (carbon and nitrogen) based reconstruction of paleodiets. ► Human remains recovered from Canimar Abajo, Matanzas Province, Cuba. ► Individuals consumed marine resource diets supplemented with terrestrial plants. ► Trophic level and isotope shifts for breastfed and weaned infant/juveniles (I/J). ► I/J evidence of weaning through distinct δ 15N enrichments and δ 13C depletions.This preliminary study investigates the diet of a population of humans (n = 28) recovered from a shell-matrix site of Canimar Abajo on the Canimar River, Matanzas Province, Cuba. The site is characterized by two cemetery levels separated by a layer of occupation/ritual/midden activity that lasted 1.5 ka. Stable C (δ 13C) and N (δ 15N) isotope analysis of human bone collagen samples obtained from individuals (7 infant/juveniles, and 21 adults) from both cemetery levels was conducted in order to reconstruct the diet of these two populations, investigate the relative importance of marine vs. terrestrial resources, and reveal any sex- and age-related distinctions in their food sources. Initial indications suggest that individuals from both cemetery levels consumed diets that were marine resource intensive but also supplemented with varied additions of terrestrial (mostly plant) resources. This supplementation is particularly evident in the later cemetery population. Though there are no significant differences in diet according to sex, there is a trophic level and terrestrial-based shift for breastfed and weaning infant/juveniles. The infant/juveniles showed evidence of being weaned through distinct δ 15N enrichments and δ 13C depletions over adult females.
Tracing stream leakage towards an alluvial aquifer in a mountain basin using environmental isotopes by J. Mas-Pla; E. Font; O. Astui; A. Menció; A. Pérez-Paricio (85-94).
► Spring data define the altitudinal isotopic gradient in the Montseny-Guilleries area. ► Runoff isotopes are defined by the altitudinal gradient and the hypsometric curve. ► Head data alone are not sufficient to define the stream–aquifer relationship. ► Stream isotopic values are thus key in identify stream recharge to the aquifer.Stream–aquifer relationships in mountain basins are of great relevance because they control the water balance and, with it, the amount of resources (whether surface water or ground water) available for ecological and human demands. In this paper, this relationship is studied using environmental isotopes (δ 18O and δD) to identify the occurrence of stream recharge in the Arbúcies River basin (NE Spain). Isotopic data from 51 natural springs define the local altitudinal gradient. This function is weighted by the proportional area above each point, given by the hypsometric curve, in order to estimate the isotopic stream water content as the contribution of runoff from incremental elevations. Stream water isotopes from two surveys are compared with hypsometrically averaged isotopic values to check for the appropriateness of this approach. Results show that it is more suitable when subsurface flows from surface formations, such as alluvial deposits, are the main contributors to stream discharge than when it derives from a single rainfall event. The characterization of stream isotope values is used as a key factor in identifying stream leakage to an unconfined alluvial aquifer in the lower reach of the Arbúcies River.
The application of isotope and chemical analyses in managing transboundary groundwater resources by Teodora Szocs; Nina Rman; Miklós Süveges; László Palcsu; György Tóth; Andrej Lapanje (95-107).
► Chemical analyses, D, O and C isotopes were used to correlate cross border aquifers. ► Water of transboundary thermal GWB Mura-Zala is of meteoric origin. ► δD (−87‰ to −75‰), δ18O (−11.9‰ to −10.4‰) and 14C (less than 6.1 pmC). ► δ13C values are shifted significantly, cannot be used for radiocarbon age corrections. ► Environmental isotopes can act as an early warning in the thermal water management.Managing transboundary groundwater resources requires accurate and detailed knowledge of aquifers and groundwater bodies. The Pannonian Basin is the largest intracontinental basin in Europe with a continuous succession of more than 7 km of Miocene to Quaternary sediments and with an average geothermal gradient of about 5 °C/100 m. Geographically the Pannonian basin overlaps eight countries (Hungary, Romania, Serbia, Croatia, Slovenia, Austria, Slovakia and Ukraine), so the issue of transboundary cold and thermal water resources is regionally very important. The T-JAM bilateral Hungarian–Slovenian (HU–SLO) project is the first to apply modern isotopic and chemical analyses in the characterization and correlation of a number of shared groundwater resources in the Mura-Zala Sub-basin of the Pannonian. The aims of this work were the identification of groundwater flow paths, the delineation of transboundary aquifers based on thermal and cold groundwater geochemical and isotope properties in the Mura-Zala Basin, and providing input to calibrate a hydraulic numerical model. Following a common groundwater sampling campaign, 24 cold and thermal groundwater samples from seven aquifers were collected for chemical, isotope, gas and noble gas analyses. Chemical analyses, and D, O and C isotopes were used to correlate cross border aquifers. A regional groundwater flow is hydrogeologically possible in some aquifers in the Mura-Zala Basin, and has been confirmed by hydrogeochemistry. The Újfalu (HU) and Mura (SLO) Formations are a part of the active regional thermal groundwater flow system, probably hydraulically separated from the shallower flow system of the Ptuj-Grad (SLO), Zagyva and Somló-Tihany (HU) Formations. The thermal water is of meteoric origin, reductive and alkaline. The predominant water type in the Quaternary and Pliocene aquifers is Ca–Mg–HCO3, changing to Na–HCO3 in the main Pannonian geothermal aquifer, and Na–Cl brine in deeper and older Miocene aquifers. Total dissolved solids and Na content generally increase with depth. Deuterium is in the range −87‰ to −75‰, 18O from −11.9‰ to −10.4‰, while 14C values are less than 6.1 pmC in the samples of the active regional thermal groundwater flow system. These and results of noble gas analyses indicate recharge during the Pleistocene interglacial period with temperatures around 6–7 °C. Regional thermal water resources are limited and environmental isotopes can be used as an early warning in the management of thermal water.
Is 222Rn a suitable tracer of stream–groundwater interactions? A case study in central Italy by L. Stellato; F. Terrasi; F. Marzaioli; M. Belli; U. Sansone; F. Celico (108-117).
► Modeling riverbank infiltration in an alluvial plain. ► 222Rn gave information about the river water residence times within the aquifer. ► TDS allowed to estimate the extent of mixing between surface waters and groundwater. ► Stream-bank infiltration velocities are smaller in the high-flow than in the low-flow period.River water infiltration into an unconfined porous aquifer (∼73% gravels, ∼12% sands, ∼15% silts and clays) in the Petrignano d’Assisi plain, central Italy, was traced combining isotopic techniques (222Rn) with hydrochemical and hydrogeologic techniques in order to characterize the system under study. The 222Rn gave information about the river water residence times within the aquifer and hydrochemical data, in a two-component mixing model, which allowed estimating the extent of mixing between surface waters and groundwater in wells at increasing distances from the river. The mixing measured in the well closer to the riverbank indicated a higher contribution of river water (up to 99%) during the groundwater recession phase and a moderate contribution (up to 64%) during the recharge phase. A model describing 222Rn concentrations in groundwater as the result of both parent/daughter nuclide equilibrium and mixing process (222Rn mixing/saturation model) was used to describe observed Rn concentrations and mixing index trends with the aim of evaluating water mean infiltration velocities along the transect. The stream bank infiltration velocities obtained by the model ranged from 1 m day−1 during groundwater recharge periods, when river water infiltration is lower, to 39 m day−1 during recession phases, when river water infiltration is larger.
Using 3H and 14C to constrain the degree of closed-system dissolution of calcite in groundwater by Ian Cartwright; L. Keith Fifield; Uwe Morgenstern (118-128).
► δ13C and 87Sr/86Sr in Ovens groundwater imply substantial carbonate dissolution. ► 3H vs. 14C imply negligible closed-system calcite dissolution. ► Calcite dissolution largely open-system process. ► Recognising open-system calcite dissolution important for dating deeper groundwater.This study uses 3H concentrations, 14C activities (a14C), 87Sr/86Sr ratios, and δ13C values to constrain calcite dissolution in groundwater from the Ovens catchment SE Australia. Taken in isolation, the δ13C values of dissolved organic C (DIC) and 87Sr/86Sr ratios in the Ovens groundwater imply that there has been significant calcite dissolution. However, the covariance of 3H and 14C and the calculated initial 14C activities (a0 14C) imply that most groundwater cannot have dissolved more than 20% of 14C-free calcite under closed-system conditions. Rather, calcite dissolution must have been partially an open-system process allowing 13C and 14C to re-equilibrate with CO2 in the unsaturated zone. Recognising that open-system calcite dissolution has occurred is important for dating deeper groundwater that is removed from its recharge area in this and other basins. The study is one of the first to use 14C and 3H to constrain the degree of calcite dissolution and illustrates that it is a valuable tool for assessing geochemical processes in recharge areas.
Multi-isotopic study (15N, 34S, 18O, 13C) to identify processes affecting nitrate and sulfate in response to local and regional groundwater mixing in a large-scale flow system by R. Puig; A. Folch; A. Menció; A. Soler; J. Mas-Pla (129-141).
► We studied a range-and-basin area where different scale flow systems converge. ► Pig manure and chemical fertilizers are the main nitrate and sulfate sources. ► Mixing between regional and local groundwater can favor denitrification processes.The integrated use of hydrogeologic and multi-isotopic approaches (δ15N, δ18ONO3, δ34S, δ18OSO4 and δ13CHCO3) was applied in the Selva basin area (NE Spain) to characterize NO 3 - and SO 4 2 - sources and to evaluate which geochemical processes affect NO 3 - in groundwater. The studied basin is within a basin-and-range physiographic province where natural hydrodynamics have been modified and different scale flow systems converge as a consequence of recent groundwater development and exploitation rates. As a result, groundwaters related to the local recharge flow system (affected by anthropogenic activities) and to the generally deeper regional flow system (recharged from the surrounding ranges) undergo mixing processes. The δ15N, δ18ONO3 and δ34S indicated that the predominant sources of contamination in the basin are pig manure and synthetic fertilizers. Hydrochemical data along with δ15N, δ18ONO3, δ34S, δ18OSO4 and δ13CHCO3 of some wells confirmed mixing between regional and local flow systems. Apart from dilution processes that can contribute to the decrease of NO 3 - concentrations, the positive correlation between δ15N and δ18ONO3 agreed with the occurrence of denitrification processes. The δ34S and δ18OSO4 indicated that pyrite oxidation is not linked to denitrification, and δ13CHCO3 did not clearly point to a role of organic matter as an electron donor. Therefore, it is proposed that the mixing processes between deeper regional and local surface groundwater allow denitrification to occur due to the reducing conditions of the regional groundwater. Thus, isotopic data add useful complementary information to hydrochemical studies, especially in those areas where hydrochemical data is not conclusive.
The role of Lower Cretaceous sediments in groundwater nitrate attenuation in central Spain: Column experiments by R. Carrey; N. Otero; A. Soler; J.J. Gómez-Alday; C. Ayora (142-152).
► A column experiment was performed to evaluate nitrate attenuation of Cretaceous strata. ► A field study shows nitrate a subset of samples partially denitrified. ► A column experiment indicates that organic matter is the main electron donor. ► The isotopic data of column samples allowed the quantification of attenuation at field scale.Endorheic basins located in semiarid or arid regions constitute one of the most vulnerable and exposed environments to NO 3 - pollution. The Pétrola basin (Central Spain) is an outstanding example of one of these endorheic system. Several constraints have been observed that impede correct identification of the denitrification pathway and its degree at the field scale. To better understand the key factors controlling NO 3 - attenuation, a five-stage column experiment was performed using organic and pyrite rich sediments from the Utrillas Facies (Lower Cretaceous) as a possible electron donor source to promote denitrification. A chemical and multi-isotopic characterization (δ15NNO3, δ18ONO3, δ13CDIC, δ34SSO4, δ18OSO4) of the outflow of the column experiment showed that NO 3 - attenuation was driven by organic matter. The amount of organic C consumed during denitrification was 2% of the total organic C present in the sediment. Both the degree and rate of denitrification were related to flow rate variations. Lower flow rates favored bacterial growth at the beginning of the experiment producing an increase of complete denitrification rate (CDR). When NO 3 - reduction was greater than 15%, CDR remained constant (around 30 μmol L−1 d−1) under different flow rates. In the last stage, flow rate had no effect on output NO 3 - concentration because the organic C supply was limited and had become the main kinetic factor in denitrification. Isotopic fractionations (ε of 15N– NO 3 - and 18O– NO 3 - between reaction products and remaining reactants were calculated using representative column samples. The results for the two attenuation stages observed were −11.6‰ and −15.7‰ for εN, and −12.1‰ and −13.8‰ for εO. Most of the field samples showed a percentage of attenuation ranging from 0% to 60% of NO 3 - removal.
Isotope characterization of an in situ biodenitrification pilot-test in a fractured aquifer by G. Vidal-Gavilan; A. Folch; N. Otero; A.M. Solanas; A. Soler (153-163).
► Lab-experiments were performed to study denitrification amendment strategy. ► An in situ pilot-test indicated biodenitrification viability in a fractured media. ► Transient accumulation of intermediate and undesired products was observed. ► Isotopic data suggested co-existance of autotrophic denitrifying activity.Laboratory and field-scale experiments were developed to test the viability of in situ heterotrophic denitrification in a fractured aquifer and were characterized using chemical, microbial and isotopic tools. Native microbiota were stimulated and NO 3 - reduction was effectively achieved by addition of a C source (ethanol or glucose) as well as a P source (disodium hydrogen phosphate). Transient NO 2 - accumulation was observed at all scales, as was some evidence for incomplete denitrification and coexistence of other respiration processes (such as Fe or SO4 reduction) and autotrophic denitrification. The N and O isotope fractionation obtained at the laboratory scale (−13.0‰ and −17.1‰ for ε N and −8.9‰ and −15.1‰ for ε O in ethanol and glucose-amended experiments, respectively), resulting in ε N/ε O values of 1.46 (ethanol-amended experiment), and 1.13 (glucose-amended), allowed the calculation of the field-scale denitrification percentage. Sulfate isotopic characterization, on the other hand, proved that autotrophic denitrification linked to sulfide oxidation could be occurring along with heterotrophic denitrification. Overall, results suggest that stimulated heterotrophic denitrification could be applied as a remedial alternative in fractured media. However, efforts must be addressed to control microbial population and stability as a key issue to avoid the decrease of groundwater quality due to incomplete denitrification or secondary respiratory processes. As demonstrated in this work, insight into such issues can be efficiently studied by means of isotopic techniques.
Hydrodynamic and isotopic characterization of a site contaminated by chlorinated solvents: Chienti River Valley, Central Italy by Marco Petitta; Eva Pacioni; Chiara Sbarbati; Gianni Corvatta; Marco Fanelli; Ramon Aravena (164-174).
► The fate of chlorinated solvents in groundwater in an alluvial aquifer has been investigated. ► Heterogeneity of the aquifer sediments causes vertical components of groundwater flow. ► Multilevel data shows the VOC’s stratification in the aquifer. ► Concentration and δ13C and δ37Cl data showed that dilution controls the VOC’s distribution. ► Biodegradation has been confirmed by isotope data only in low permeability layers.Contaminant sources have been attributed to shoe manufacturers in an alluvial aquifer located along 26 km2 in the Chienti River Valley, Central Italy. During the 1980s and 1990s, the main chlorinated compound used in the study area was 1,1,1-Trichloroethane (1,1,1-TCA), which was substituted by Perchloroethene (PCE) in the last 15 years. A hydrogeological conceptual model has been developed for the alluvial aquifer taking into account the presence of low permeability lenses, forming a multilayer semi-confined aquifer. Hydrodynamic tests (pumping and flowmeter heat-pulse tests) coupled with standard and multilevel hydrochemical and isotopic samplings were performed. Flowmeter tests showed the existence of vertical flow between aquifer levels having different permeability. Physical–chemical parameter logs agreed with the existence of a multilayer aquifer. Concentration data collected in 21 wells located downgradient of the different sources revealed VOC (Volatile Organic Compound) levels lower than 100 μg/L in the upper part of the valley and levels reaching about 200 μg/L in the near shore areas. PCE is the main compound present in the aquifer. No evidence of the presence of TCA was found in the upper areas of the Chienti Valley, but in the areas near the shore, TCA and its degradation products are predominant. Data collected at multilevels located at two sites (upper and near shore areas) to refine the results obtained in the regional survey show a stratification of the VOC concentrations; values of each compound are higher than those measured in the conventional wells during the standard sampling (e.g. PCE: 150 μg/L instead of 2 μg/L). In addition, the vertical distribution of the contaminant reflects the vertical flow pattern inferred from hydrogeological data. The hydrogeological, VOC and isotope data showed that dilution is the main process controlling VOCs concentration in the aquifer. Degradation also played a role in the attenuation of the parent compounds in some localized areas of the aquifer. The role of the low permeability layers on VOC degradation was documented by the presence of cis-1,2-DCE, a main daughter product of PCE, in some zones of the upper area, and 1,1-Dichloroethene (1,1-DCE) and 1,1-Dichloroethane (1,1-DCA), byproducts of 1,1,1-TCA degradation, in the near shore areas.
Cl and C isotope analysis to assess the effectiveness of chlorinated ethene degradation by zero-valent iron: Evidence from dual element and product isotope values by Carme Audí-Miró; Stefan Cretnik; Neus Otero; Jordi Palau; Orfan Shouakar-Stash; Albert Soler; Martin Elsner (175-183).
► TCE and cis-DCE Cl isotope fractionation was investigated for the first time with ZVI. ► A C–Cl bond is broken in the rate-limiting step during ethylene ZVI dechlorination. ► Dual C/Cl isotope plot is a promising tool to discriminate abiotic degradation. ► Product-related carbon isotopic fractionation gives evidence of abiotic degradation. ► Hydrogenolysis and β-dichloroelimination pathways occur simultaneously.This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (TCE) and cis-dichloroethene (cis-DCE) during reductive dechlorination by cast zero-valent iron (ZVI). Hydrogenolysis and β-dichloroelimination pathways occurred as parallel reactions, with ethene and ethane deriving from the β-dichloroelimination pathway. Carbon isotope fractionation of TCE and cis-DCE was consistent for different batches of Fe studied. Transformation of TCE and cis-DCE showed Cl isotopic enrichment factors (ε Cl) of −2.6‰ ± 0.1‰ (TCE) and −6.2‰ ± 0.8‰ (cis-DCE), with Apparent Kinetic Isotope Effects (AKIECl) for Cl of 1.008 ± 0.001 (TCE) and 1.013 ± 0.002 (cis-DCE). This indicates that a C–Cl bond breakage is rate-determining in TCE and cis-DCE transformation by ZVI. Two approaches were investigated to evaluate if isotope fractionation analysis can distinguish the effectiveness of transformation by ZVI as opposed to natural biodegradation. (i) Dual isotope plots. This study reports the first dual (C, Cl) element isotope plots for TCE and cis-DCE degradation by ZVI. The pattern for cis-DCE differs markedly from that reported for biodegradation of the same compound by KB-1, a commercially available Dehalococcoides-containing culture. The different trends suggest an expedient approach to distinguish abiotic and biotic transformation, but this needs to be confirmed in future studies. (ii) Product-related isotope fractionation. Carbon isotope ratios of the hydrogenolysis product cis-DCE differed consistently by 10‰ compared to the β-dichloroelimination products ethene and ethane providing a second line of evidence to differentiate abiotic or biotic degradation pathways.
Coal fly ash interaction with environmental fluids: Geochemical and strontium isotope results from combined column and batch leaching experiments by Tonya M. Brubaker; Brian W. Stewart; Rosemary C. Capo; Karl T. Schroeder; Elizabeth C. Chapman; Lev J. Spivak-Birndorf; Dorothy J. Vesper; Carol R. Cardone; Paul C. Rohar (184-194).
► Element release during fly ash extraction experiments controlled by mineralogy. ► Strontium isotopes in fly ash are not homogenized during coal combustion. ► Element correlations with 87Sr/86Sr indicate chemically resistant silicate phase. ► Sr isotopes can uniquely identify fly ash fluids leaking into the environment.The major element and Sr isotope systematics and geochemistry of coal fly ash and its interactions with environmental waters were investigated using laboratory flow-through column leaching experiments (sodium carbonate, acetic acid, nitric acid) and sequential batch leaching experiments (water, acetic acid, hydrochloric acid). Column leaching of Class F fly ash samples shows rapid release of most major elements early in the leaching procedure, suggesting an association of these elements with soluble and surface bound phases. Delayed release of certain elements (e.g., Al, Fe, Si) signals gradual dissolution of more resistant silicate or glass phases as leaching continues. Strontium isotope results from both column and batch leaching experiments show a marked increase in 87Sr/86Sr ratio with continued leaching, yielding a total range of values from 0.7107 to 0.7138. For comparison, the isotopic composition of fluid output from a fly ash impoundment in West Virginia falls in a narrow range around 0.7124. The experimental data suggest the presence of a more resistant, highly radiogenic silicate phase that survives the combustion process and is leached after the more soluble minerals are removed. Strontium isotopic homogenization of minerals in coal does not always occur during the combustion process, despite the high temperatures encountered in the boiler. Early-released Sr tends to be isotopically uniform; thus the Sr isotopic composition of fly ash could be distinguishable from other sources and is a useful tool for quantifying the possible contribution of fly ash leaching to the total dissolved load in natural surface and ground waters.
Chemical and lead isotope constraints on sources of metal pollution in street sediment and lichens in southwest Ohio by Erin LeGalley; Elisabeth Widom; Mark P.S. Krekeler; David C. Kuentz (195-203).
► Urban pollution study in a neighborhood adjacent to a coal-fired power plant. ► Pb isotopic compositions determined in street sediment and lichen samples. ► Geochemistry is consistent with Pb contamination from yellow road paint containing PbCrO4.Lead isotopic compositions were determined in street sediment and lichen samples to constrain the sources of metal pollution near a coal-fired power plant in SW Ohio. Previous studies of the street sediment found elevated levels of Cr, Cu and Ni, and extremely high levels of Pb and Zn. Although initial investigations suggested the presence of coal-derived pollution, Pb isotopes were employed to investigate the importance of additional sources. Highly variable concentrations of Pb in sieved (<38 μm) street sediment and lichen samples range from 130 to 1399 ppm and 11 to 53 ppm, respectively. Street sediment and lichen samples exhibit a strong positive correlation of 208Pb/204Pb vs. 206Pb/204Pb, 208Pb/206Pb vs. 207Pb/206Pb, 207Pb/206Pb vs. 206Pb/204Pb, and 207Pb/204Pb vs. 206Pb/204Pb consistent with Pb contamination from road paint containing PbCrO4 as a yellow pigment. Extremely high concentrations of Pb in road paint samples (812–6305 ppm) suggest road paint containing PbCrO4 is a major contributor to Pb levels in urban environments. Additional sources fro Zn and Cu beyond pollution derived from coal and road paint are proposed. Fine particulates containing potentially harmful metals in street sediment may be re-suspended in the air, as suggested by their presence in lichens, and pose a respiratory risk to human health. These metals may pose a risk to the greater environment, such as aquatic ecosystems subject to stormwater discharge from urban areas. This study is relevant and applicable to other urban settings, and prevention and remediation strategies for contaminated street sediment are recommended.
Copper and iron isotope fractionation in mine tailings at the Laver and Kristineberg mines, northern Sweden by Nathalie Pérez Rodríguez; Emma Engström; Ilia Rodushkin; Peter Nason; Lena Alakangas; Björn Öhlander (204-215).
► Describes Cu and Fe isotope fractionation in subarctic mine tailings. ► Covellite precipitated from pyrrhotite oxidation is depleted in 65Cu. ► Adsorption of 65Cu in organic layers in natural samples. ► Pyrite oxidation is linked to a enrichment in 56Fe in oxidising tailings.Previous research has shown that Cu and Fe isotopes are fractionated by dissolution and precipitation reactions driven by changing redox conditions. In this study, Cu isotope composition (65Cu/63Cu ratios) was studied in profiles through sulphide-bearing tailings at the former Cu mine at Laver and in a pilot-scale test cell at the Kristineberg mine, both in northern Sweden. The profile at Kristineberg was also analysed for Fe isotope composition (56Fe/54Fe ratios). At both sites sulphide oxidation resulted in an enrichment of the lighter Cu isotope in the oxidised zone of the tailings compared to the original isotope ratio, probably due to preferential losses of the heavier Cu isotope into the liquid phase during oxidation of sulphides. In a zone with secondary enrichment of Cu, located just below the oxidation front at Laver, δ65Cu (compared to ERM-AE633) was as low as −4.35 ± 0.02‰, which can be compared to the original value of 1.31 ± 0.03‰ in the unoxidised tailings. Precipitation of covellite in the secondary Cu enrichment zone explains this fractionation. The Fe isotopic composition in the Kristineberg profile is similar in the oxidised zone and in the unoxidised zone, with average δ56Fe values (relative to the IRMM-014) of −0.58 ± 0.06‰ and −0.49 ± 0.05‰, respectively. At the well-defined oxidation front, δ56Fe was less negative, −0.24 ± 0.01‰. Processes such as Fe(II)–Fe(III) equilibrium and precipitation of Fe-(oxy)hydroxides at the oxidation front are assumed to cause this Fe isotope fractionation. This field study provides additional support for the importance of redox processes for the isotopic composition of Cu and Fe in natural systems.